This invention relates generally to the field of passive solar energy systems, and in particular, to a solar window panel having light transmitting and light reflecting properties which vary in relation to the seasons of the year.
An effective solar window for a passive solar heated structure should possess the following characteristics, especially for space heating of that structure:
1. During the winter months, solar radiation should be permitted to pass through the window, and into the structure;
2. During the summer months, solar radiation should be prevented from passing through the window, and into the structure;
3. At all times, but particularly during the winter months, the solar window should insulate against conductive-convective-reradiative heat loss from the structure; and
4. At all time, but particularly during the summer months, the solar window should insulate against conductive-convective-reradiative heat gains within the structure, when the outside ambient temperature is greater than that desired inside the structure.
Ordinary single glazed panels (glass or plastic) only provide the first characteristic, failing to provide the remaining characteristics.
Multiple glazed panels have been produced to improve this result. A double glazed panel will provide the first characteristic above mentioned, and will at least in part, assist in providing the third and fourth characteristics. However, the second characteristic is not provided.
A triple glazed panel improves upon the results obtained using a double glazed panel, however, the second characteristic is still not provided. Moreover, the cost of producing a triple glazed panel, using the present techniques of manufacture, becomes prohibitive, reducing its costs effectiveness as an energy system.
In an effort to further improve upon the performance of multiple glazed panels, there have also beeen produced double-walled, ribbed glazed panels. Two commercially available examples of these structures are manufactured by CY/RO Industries ("Acrylite" SDP [acrylic] and Polycarbonate SDP sheet), and by Rohm and Haas Co. ("Tuffak Twinwall" polycarbonate). While these structures provide the first, third and fourth characteristics, the second characteristic still is not provided.
Irrespective of which of the above glazed panels is used, a structure, particularly one having unshaded, south vertical or sloping windowed walls or roofs, invariably became overheated in the warmer months. Structural overhangs, reflective drapes, venetian blinds, and shades have been used in an attempt to reduce this overheating problem. However, such measures are only partially effective, involve relatively complex and expensive structures, and is some applications, cannot be readily used, e.g., greenhouses.
Recognizing the shortcomings of the above mentioned glazed panels, there have been developed panels having light transmitting and light reflecting properties which respond to the solar altitude. These panels generally comprise an inner and an outer glazed panel or face between which are positioned a plurality of longitudinally extending vanes. These vanes are provided with means for reflecting or filtering solar radiation, which means interact with the vanes and the glazed panels to provide, at least in part, the above identified four characteristics. Examples of such panels may be found, for example, in U.S. Pat. Nos. 4,091,592; 4,035,539; 3,940,896; 3,642,557; 3,077,643; 3,059,537; 2,874,611; and 2,849,762.
Although such vaned-glazed panels provide improved results in obtaining the four characteristics necessary to produce an effective solar window, such panels exhibit several disadvantages which seriously impair their ultimate utility as a passive solar energy system.
The primary disadvantage exhibited by such panels is that they invariably require the assembly of discrete components to produce the desired result. Generally such panels comprise a separate pair of glazed panels, having positioned therebetween a third assembly, which assembly comprises a plurality of discretely produced vanes. This results in an assembly of numerous components to produce a single solar window. The disadvantages of this are many.
Cost is an extremely important factor in producing a commercially acceptable passive solar energy system. The costs of production necessarily rise in proportion to both the number of discrete components needed to produce the panel, as well as the number of steps that are required to assemble that panel. Consequently, such multi-component panels are not cost competitive with any savings in heating and cooling costs which they may ultimately afford.
Another factor which is related to cost is the useful life of such panels. For a panel to be commercially acceptable, it must be capable of providing a useful life which is sufficient to prevent unnecessary, repetitive replacement of the panels. However, the panels above mentioned are an assemblage of discrete components, many of which are formed of different materials, giving rise to the potential for the uneven expansion and contraction of these components as the temperature of their environment changes. Such uneven expansion and contraction could eventually result in the failure of such panels, impairing their useful life. This problem becomes even more acute when such panels are mounted in rigid window mounting frames which further restrict their expansion and contraction, or when such panels are used as roofing sections, to form a skylight.
Coupled to the above problems is that of initially installing, as well as repairing, such panels. A panel comprising a plurality of discrete components requires additional care in its installation, to assure proper alignment of the components, as well as to insure proper operation of the window. These problems are also present when a given panel requires replacement. Such additional problems result in increased costs in installing such a system, and in repairing that system, further reducing its commercial acceptability.
A last factor is that of esthetics. Ideally a window should be functional without detrement to its pleasing visual effect, an objective not easy to attain.
A commercially acceptable solar window panel which is capable of providing all four of the energy transmitting, energy reflecting, and heat insulative properties required for proper operation of the resulting passive solar energy system has not yet been produced.